java.lang.RuntimeException:无法实例化 Kotlin MainActivity 的活动 Com

Question

这是我第一次使用 kotlin，出于某种原因，我不得不在我的 MainActivity 中使用 kotlin 语言。 我通过代码将我的 MainActivity 类更改为 kotlin 文件-> 将 Java 文件转换为 Kotlin 文件但是当我运行代码时，我会收到以下错误：

java.lang.RuntimeException: Unable to instantiate activity 
ComponentInfo{ir.mohammadhf.sevenautoshow/ir.mohammadhf.sevenautoshow.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "ir.mohammadhf.sevenautoshow.MainActivity" on path: DexPathList[[zip file "/data/app/ir.mohammadhf.sevenautoshow-b4uU0l0_OCV9z_7YwD1uHg==/base.apk"],nativeLibraryDirectories=[/data/app/ir.mohammadhf.sevenautoshow-b4uU0l0_OCV9z_7YwD1uHg==/lib/x86, /data/app/ir.mohammadhf.sevenautoshow-b4uU0l0_OCV9z_7YwD1uHg==/base.apk!/lib/x86, /system/lib, /system/vendor/lib]]
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2718)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.ClassNotFoundException: Didn't find class "ir.mohammadhf.sevenautoshow.MainActivity" on path: DexPathList[[zip file "/data/app/ir.mohammadhf.sevenautoshow-b4uU0l0_OCV9z_7YwD1uHg==/base.apk"]

我搜索了类似的问题，但在大多数问题中，他们建议"在Android清单中声明活动"。但它已经为我完成了。

这是我的清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="ir.mohammadhf.sevenautoshow">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:name=".App"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:testOnly="false"
android:theme="@style/AppTheme"
android:usesCleartextTraffic="true">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

这是我的主要活动：

class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
}

和 Build.gradle：

apply plugin: 'com.android.application'
android {
compileSdkVersion 28
buildToolsVersion "29.0.1"
defaultConfig {
applicationId "ir.mohammadhf.sevenautoshow"
minSdkVersion 19
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
multiDexEnabled true
vectorDrawables.useSupportLibrary true
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.0.2'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
implementation 'com.google.android.material:material:1.0.0'
implementation "androidx.core:core-ktx:+"
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.21"
}
repositories {
mavenCentral()
}

我错过了什么吗？

---

此问题的解决方案

把这个代码放在项目build.gradle中：

buildscript {
ext.kotlin_version = '1.3.21'
repositories {
google()
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:3.4.1'
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}

}

然后将这些插件添加到您的模块build.gradle中：

apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-android'

然后同步，它会将 kotlin 的插件添加到您的 Java 项目中

Answer 1

尝试在开始时在build.gradle文件中应用kotlin。

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-kapt'
android {
compileSdkVersion 28